Interpretive Summary: Stripe rust is one of the most important diseases of wheat worldwide. The best strategy to control stripe rust is to grow resistant cultivars. One such cultivar resistant to most races in North America is ‘IDO377s’, but its gene or genes for stripe rust was unknown. A genetic and molecular mapping study was conducted to identify the resistance gene(s). The genetic analysis showed that IDO377s caries a single dominant gene for resistance. The gene was mapped to the long arm of chromosome 2B using molecular markers and was determined to be different from previously named genes for stripe rust resistance in wheat. Therefore, we officially named the gene in IDO377s as Yr43 and also named a gene for stripe rust resistance in wheat cultivar Zak as Yr44. The genetic linkage of the genes and their linkages to Yr5, another wheat genes previously identified on the long arm of chromosome 2B were determined. Testing 108 wheat cultivars and breeding lines with two markers flanking the Yr43 gene in IDO377s at genetic distances of 5.5 and 4.4 cM validated the presence and absence of the gene in the wheat egnotypes and showed the usefulness of the markers in marker-assisted for incoporating the resistance gene in IDO377s to wheat cultivars and combine with other genes for durable effective resistance to stripe rust. The genes named in this study are also useful in monitoring virulence changes in the rust population and understanding interactions between wheat and the stripe rust pathogen.

Technical Abstract:
Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most important diseases of wheat worldwide. The best strategy to control stripe rust is to grow resistant cultivars. One such cultivar resistant to most races in North America is ‘IDO377s’. To study the genetics of its resistance this spring wheat cultivar was crossed with ‘Avocet Susceptible’ (AvS). Seedlings of the parents, F2 plants, and F3 lines were tested under controlled greenhouse conditions with races PST-43 and PST-45 of P. striiformis f. sp. tritici. IDO377s caries a single dominant gene for resistance. Resistance gene analog polymorphism (RGAP) and simple sequence repeat (SSR) techniques were used to identify molecular markers linked to the resistance gene. A total of 10 markers were identified, two of which flanked the locus at 5.5 and 4.4 cM. These flanking RGAP markers were located on chromosome 2B with nulli-tetrasomic lines of ‘Chinese Spring’. Their presence in the ditelosomic 2BL line localized them to the long arm. The chromosomal location of the resistance gene was further confirmed with two 2BL- specific SSR markers and a sequence tagged site (STS) marker previously mapped to 2BL. Based on the chromosomal location, reactions to various races of the pathogen and tests of allelism, the IDO377s gene is different from all previously designated genes for stripe rust resistance, and is therefore designated Yr43. A total of 108 wheat breeding lines and cultivars with IDO377s or related cultivars in their parentage were assayed to assess the status of the closest flanking markers and to select lines carrying Yr43. The results showed that the flanking markers were reliable for assisting selection of breeding lines carrying the resistance gene. A linked stripe rust resistance gene, previously identified as YrZak, in cultivar Zak was designated Yr44.